1. Field of the Invention
The present invention relates to an objective lens driving device. In particular, the present invention relates to an objective lens driving device used in a recording and reproducing apparatus that irradiates an optical spot on a disk-like recording medium and records and/or reproduces information optically. Also, the present invention relates to an optical disk apparatus including such an objective lens driving device.
2. Description of Related Art
In a conventional objective lens driving device, an objective lens for forming an optical spot on a recording surface of a disk is driven and translated in a direction perpendicular to the disk surface (hereinafter, referred to as a “focusing direction”) and a radial direction of the disk (hereinafter, referred to as a “tracking direction”). An optical disk apparatus developed in response to densification is provided with a function of correcting an optical coma aberration in order to achieve excellent recording and reproducing characteristics. For this purpose, it is necessary to drive the objective lens not only in the focusing direction and the tracking direction but also in a direction rotating around an axis parallel with a direction tangent to the circumference of the disk (or to a recording track on the disk) (hereinafter, referred to as a “radial tilting direction”). Such an objective lens driving device is disclosed in JP 11(1999)-283258 A, for example. In the following, by taking the technology disclosed in this document as an example, a conventional objective lens driving device will be described with reference to the accompanying drawings.
FIG. 6 is a perspective view showing a configuration of the conventional objective lens driving device, and FIG. 7 is a plan view showing the arrangement of coils and magnets in the conventional objective lens driving device. In FIGS. 6 and 7, an arrow Fo indicates a focusing direction, an arrow Tr indicates a tracking direction, an arrow Ti indicates a radial tilting direction, and an arrow S indicates a direction tangent to the circumference of a disk, which is not shown in the figures (or to a recording track on the disk) (hereinafter, referred to as a “circumferential direction”).
Focusing coils 54L and 54R and a tracking coil 55 are fixed firmly to a lens holder 52 that holds an objective lens 51, thus constituting a movable portion 64. One end of each of elastically-deformable supports 53a, 53b, 53c and 53d is fixed firmly to the lens holder 52, while the other end thereof is fixed firmly to a fixing portion 62, so that the movable portion 64 is supported in a manner translatable in the focusing direction Fo and the tracking direction Tr and rotatable in the radial tilting direction Ti. Further, the fixing portion 62 is fixed to a supporting base 63.
Magnets 58 and 59 are arranged so as to face each other and attached to yokes 56a and 56b, respectively, thus constituting a magnetic circuit 65R. In a magnetic gap between the magnets 58 and 59, the focusing coil 54R and the tracking coil 55 are arranged. Similarly, magnets 60 and 61 are arranged so as to face each other and attached to yokes 57a and 57b, respectively, thus constituting a magnetic circuit 65L. In a magnetic gap between the magnets 60 and 61, the focusing coil 54L and the tracking coil 55 are arranged. By an interaction between these two magnetic circuits 65R, 65L and an electric current passed through the focusing coils 54L and 54R and the tracking coil 55, namely, an electromagnetic force, a driving system is formed. The electric current is supplied to the focusing coils 54L and 54R and the tracking coil 55 via the supports 53a, 53b, 53c and 53d. 
Next, the arrangement of these coils and magnetic poles of the magnets will be described referring to FIG. 7. The magnets 58 and 59 are both magnetized in the same direction as the arrow S (the circumferential direction of the disk) and supply a magnetic flux J1. On the other hand, the magnets 60 and 61 are magnetized in the direction opposite to the arrow S and supply a magnetic flux J2. Other than the main magnetic fluxes J1 and J2, a leakage magnetic flux H1 is generated between the yokes 56a and 57a and a leakage magnetic flux H2 is generated between the yokes 56b and 57b because the magnetic circuits 65R and 65L are arranged close to each other.
The following is a description of an operation of the conventional objective lens driving device constituted as above, with reference to the accompanying drawings. In FIG. 7, when an electric current I1 is supplied to the focusing coil 54R, an electromagnetic force in the focusing direction Fo is generated in a part subjected to the magnetic flux J1 (a point P1) according to the Fleming's rule. Similarly, when an electric current 12 is supplied to the focusing coil 54L, an electromagnetic force in the focusing direction Fo is generated in a part subjected to the magnetic flux J2 (a point P2). As a result, the movable portion 64 is driven in the focusing direction Fo. However, an electromagnetic force in a direction opposite to the focusing direction Fo is generated in a part subjected to the leakage magnetic flux H1 (a point P3).
In terms of driving in the radial tilting direction Ti, a moment generated by a difference between the electric current 11 and the electric current 12, namely, a difference between the electromagnetic force in the focusing direction Fo acting on the focusing coil 54R and that acting on the focusing coil 54L allows the movable portion 64 to tilt.
Since the operation of passing an electric current thorough the tracking coil 55 so as to generate an electromagnetic force is similar to that for the focusing coils 54R and 54L, the description thereof will be omitted here.
In the conventional objective lens driving device constituted as above, the electromagnetic force in a direction opposite to the focusing direction Fo is generated in the part subjected to the leakage magnetic flux H1. Accordingly, rotating vibrations around the tracking direction Tr, so-called pitching vibrations, occur in the movable portion 64 including the objective lens 51, so that an aberration of an optical spot is generated, which causes a problem in recording and reproducing.